1. Field of the Invention
The present invention relates to a process for making a porous body of calcium phosphate, and more particularly to a process for making a porous sintered body of calcium phosphate having continuous and fine pores distributed uniformly throughout the body.
2. Prior Art
Porous bodies of ceramics, including a porous body of calcium phosphate, have hitherto been used for fillers to be filled in defects or hollow portions of bones, carriers for carrying catalysts or filter materials. Reference should be made to, for example, British Pat. No. 1,455,360, U.S. Pat. No. 4,149,894, U.S. patent application Ser. No. 191,894 now abandoned, Apr. 1, 1982, and U.S. patent application Ser. No. 261,085 filing date May 7, 1981. In the known process for making a porous body of ceramics, an organic porous body made of foamed polyurethane and having continuous void channels is dipped into a slurry of a material for ceramics to allow the slurry to adhere on the internal walls of the continuous void channels, and then the organic porous body is heated to decompose the organic material forming the porous body and concurrently to sinter the adhering material for ceramics to obtain a porous sintered body of ceramics. However, in this known process, a certain portion of the void channel in the organic porous body frequently gets clogged by the slurry of the material for ceramics. Once some portion of the void channel has gotten clogged, the slurry is prevented from getting deeper into the channel beyond the clogged portion. As a result of uneven distribution of slurry in the void channels of the organic porous body, it is difficult to obtain a porous sintered body of ceramics having continuous pores distributed uniformly throughout the resultant porous ceramic body. The tendency of clogging is disadvantageously increased as the void channels of the organic porous body become finer. In the extreme case, a slurry of ceramic material can scarcely adhere on nowhere of the internal walls of the void chanels. Due to this clogging problem, a porous body of ceramics having continuous pores of very small dimension could not be made by the known process.
In order to solve this clogging problem, it has been proposed to apply a centrifugal force to the organic porous body after dipping the same into the slurry of ceramic material or to squeeze the organic porous body through a roller assembly. However, by these centrifugalizing or squeezing methods, it was difficult to remove the slurry of ceramic material only at the clogged portion. When treated by such methods, considerable parts of the slurry of ceramic material adhering on the internal walls of the void channels of the organic porous body are removed, leading to reduction in strength of the resultant porous body of ceramics. Thus, the network of the porous sintered body of ceramics thus produced is so weak that it cannot withstand the external forces applied in practical use.
With the aim to improve the strength of the finished product of ceramic material, it has been tried to use finer particles of ceramic material in preparation of the slurry.
However, when the viscosity of the slurry is increased by using the particles of smaller size, the slurry will adversely aggravate the tendency of clogging. On the other hand, if the ceramic particles of coarser size are used to lower the density of slurry, the strength of the resultant porous body of ceramics is reduced. Thus, increase in strength of the porous body conflicts with prevention of clogging in the preparation step, and these conflicting requirements cannot be satisfied by varying the particle size of the ceramic material.
It has been further proposed to process the internal walls of the void channels of the organic porous body in order to allow the walls to be rugged so as to improve the adsorption property thereof for holding the slurry of ceramic material. This proposal involves a disadvantage that an additional processing step is necessitated. Nevertheless, the problem of clogging of the slurry of ceramic material in fine channels of the organic porous body cannot be solved by this proposal.
As has been mentioned above, in any of the known processes for making a porous ceramic body, the slurry of ceramic material cannot adhere uniformly on the walls of fine void channels of the organic porous body due to the clogging problem. In accordance with any of the prior art process, it is impossible to make a porous sintered body of ceramics having continuous and fine pores distributed uniformly throughout the porous body and having a satisfactory strength.